Accounting requires accurate arithmetic to provide reliable information. Cross-footing is a method accountants use to verify that all the numbers add up. In accounting lingo, summing a column of numbers is called footing. To cross-foot is to ensure that the sum of column totals equals the grand total.
Spreadsheets lay out numbers in rows and columns, each of which can be totaled. Imagine a sheet showing monthly sales revenue for five products over the course of a year. Each of the five rows reports one product and each of the 12 columns reports one month. A sixth row totals the month's sales and a 13th column sums the annual sales per product. Cross-footing verifies that the sum of the monthly sales in row 6 equals the sum of the annual sales per product in column 13. This sum is the grand total, located in row 6, column 13.